The present invention concerns an equipment for the conveying, edging or tapering of at least one edge of body cans, in particular but not exclusively cylindrical body metal cans, made by sealing their respective overlapping longitudinal edges or by drawing and re-drawing, and the method for conveying and edging or tapering one or both of the two edges of the respective can body.
In the metal cylindrical body can production sector (products normally used for foodstuffs, preserves and drinks), one of the most delicate stages is the definition of the circular edges of can bodies; these edges must, in fact, be "deformed" so that, in the first instance, they have an arched profile with diameter larger than the diameter of the cylindrical section of the can body; (the said operation is called edging), alternatively, an inward narrowing of the edge towards the internal surface of the said body (this operation is called tapering).
To obtain these edge shapes, machines equipped for the corresponding plastic deformation techniques are used, the equipment selected in accordance with the dimensions of the can bodies to be worked: for edging the respective two edges of can bodies, either a pair of opposing shaped pads or a or a pair opposing rotating heads with numerous shaped pads or a or a pair opposing rotating heads with numerous shaped rollers are used, whilst for tapering, traversing shaped pads only are used, described in further detail below.
Machines which use such equipment generally have a can body feeder station which supplies them to an individual can body pick-up station, also used to position the can body at an edging station. This station consists of traversing shaped pads or traversing-rotating heads with rollers: the case examined herein concerns the first of these two types of equipment.
The said equipment consists of two cylindrical operating heads, positioned opposite one another, each with a shaped pad whose profile defines the `negative" of the profile to be created on the edge if the can body; each operating head is supported by a respective shaft which moves along longitudinal axis so that the two operating heads can be moved towards and away from each other. For tapering, an internal pad is employed, with axial movement relative to the operating head, and which determines the extent to which the external edge is tapered, and facilitates removal of the can body from the relative shaped pads.
In practice, the can body is, therefore, placed between the two shaped pads, its longitudinal axis placed coaxially to the pads' traversing axis; the shaped pads are then moved towards the can body, fixed in the said position, until they gradually make contact with the respective edges of the can body with enough force to obtain the desired plastic deformation of the edges when the two shaped pads reach the limit or their forward travel
This "pad" edging or tapering technique, however, limits the diameter and thickness of the can body, since the force necessary to obtain plastic deformation of the can body edges, being simultaneously distributed on the entire edge circumference, is greater than that applied using the traversing and rotating rollers which, in contrast, cause "punctiform" deformation of the edge surface; pad edging, for example, is carried out on cans with a larger diameter which, if they are of suitable thickness, bear the force applied to the entire end without problems. As well as this size limitation, it has been observed that, during pad edging, and especially where can bodies have reduced diameter and thickness, buckling or abnormal plastic deformation may occur on the edge where the edge joins the aforementioned can body longitudinal edges.